/Engine/Source/Runtime/GeometryCore/Public/TriangleTypes.h
More robust (because it doesn't multiply orientation test results) inside-triangle test for oriented triangles only (the code early-outs at the first 'outside' edge, which only works if the triangle is oriented as expected)
1 if outside, -1 if inside, 0 if on boundary
int IsInsideOrOn_Oriented ( const [TVector2](API\Runtime\Core\Math\TVector2)< RealType > & QueryPoint ) const